1. Field of the Invention
The present invention relates to a laser scanning unit used in an image forming apparatus, and more particularly, to a laser scanning unit simplified in construction and reducing the manufacturing processes.
2. Description of the Related Art
Generally, a laser scanning unit, provided in an electrophotographic image forming apparatus such as a photocopier or a printer, forms an electrostatic latent image by projecting a laser beam onto an electrically charged photosensitive medium.
The so-called ‘tandem’ type laser scanning unit, used in an image forming apparatus capable of color-printing, generates a plurality of laser beams and projects the laser beams to a plurality of photosensitive drums, respectively and simultaneously. One example of such a laser scanning unit is disclosed in U.S. Pat. No. 6,396,615, which includes a light source unit generating the laser beams, a polygon mirror reflecting the laser beams, a mirror group having a plurality of mirrors, and fθ lens group having a plurality of lenses. The light source unit is provided with a plurality of laser diodes and collimating lenses corresponding to the laser diodes. The laser beams generated at the respective laser diodes pass through the collimating lens and a cylinder lens and are projected onto the polygon mirror. The polygon mirror deflects four laser beams within a range of a predetermined angle while rotating at a high speed. Then, the laser beams, deflected by the polygon mirror, pass through first and second lenses of the fθ lens group, and are reflected by mirrors arranged on the optical axes of the laser beams in different directions, respectively. The reflected laser beams pass through a third lens of the fθ lens group arranged on the respective optical axes, and are projected onto the photosensitive drum.
However, in the conventional laser scanning unit, there are many lenses arranged on the optical axes from the laser diodes to the photosensitive drums, such as collimating lenses, cylinder lens, and lenses of the fθ lens group, and the arrangement of mirrors for reflecting the laser beams to the photosensitive drums is also complicated. Therefore, there is a problem of increasing manufacturing costs and manufacturing processes.